Improvement in Creep Damage Tolerance of 14Cr-15Ni-Ti Modified Stainless Steel by Addition of Minor Elements

Creep properties of 14Cr-15Ni-Ti modified steel, alloyed with phosphorus and silicon were investigated at 973 K in the stress range 175-250 MPa. The phosphorus content in the alloys was 0.025 and 0.04 wt.%, silicon 0.75 and 0.95 wt.% and titanium in the range 0.16-0.3wt.%. The variation between minimum creep rate and rupture life for these alloys was found to follow the Modified Monkman Grant relationship. The inverse of Modified Monkman Grant relationship which is defined as the damage tolerance parameter was found to be above ten for these alloys, indicating that these alloys can withstand high strain concentrations. Optical microscopic investigations revealed extensive matrix deformation and precipitation. Creep damage in the form of cracks or cavities was not observed in these alloys corroborating high tolerance for creep damage. Addition of boron was found to prevent grain boundary damage.